Flower

UXL Encyclopedia of Science
COPYRIGHT 2002 The Gale Group, Inc.

Flower

A flower is the reproductive part of a plant that produces seeds. Plants that produce flowers and fruit are called angiosperms. There are more than 300,000 species of angiosperms, and their flowers and fruits vary significantly. Flowers and fruits are among the most useful features for identifying plant species.

Study of flowers throughout history

Many modern cultures consider flowers attractive, and scholars have been fascinated with flowers for thousands of years. Dioscorides, a first-century Greek physician, wrote the most influential early book on plants, De materia medica. This was the first text about the medicinal uses of plants, and it contained many diagrams of plants and their flowers. The book helped other physicians identify the species of plant to prescribe to their patients for a particular ailment. De materia medica remained an important reference on botany (the study of plants) for more than 1,500 years.

In the mid-1700s, Swedish botanist Carolus Linnaeus revolutionized the field of botany. He classified plant species according to the morphology (form and structure) of their flowers and fruits. Modern botanists continue to rely upon his classification system.

Up until the late 1700s, people believed that flowers with beautiful colors and sweet smells were created by God to please humans. However, German botanist Christian Konrad Sprengel disputed this view. He held that the characteristics of flowers (shape, color, smell) are related to their method of reproduction. Sprengel published his theory of flowers in 1793 in The Secret of Nature Revealed. Although not widely accepted in his own time, Sprengel's views were soon considered scientifically correct.

Words to Know

Angiosperm: Plant that produces flowers and seeds.

Anther: Top part of the stamen that produces pollen.

Filament: Stalk of the stamen that bears the anther.

Corolla: Layers of petals in a flower.

Morphology: Branch of biology dealing with the form and structure of living organisms.

Ovary: Base part of the pistil that bears ovules and develops into a fruit.

Ovule: Structure within the ovary that develops into a seed after fertilization.

Petal: Whorl of a flower just inside the sepals that is often colored.

Pistil: Female reproductive organ of flowers that is composed of the stigma, style, and ovary.

Pollination: Transfer of pollen from the male reproductive organs to the female reproductive organs of a plant.

Sepal: External whorl of a flower that is typically leaflike and green.

Stamen: Male reproductive organ of flowers that is composed of the anther and filament.

Stigma: Top part of the pistil upon which pollen lands and germinates.

Style: Stalk of the pistil that connects the stigma to the ovary.

Parts of the flower

There are considerable differences among the many species of flowers. Flowers can develop on different places on a plant. Terminal flowers, like a tulip, are single flowers that bloom at the apex or end of an upright stalk. Other flowers arise in an inflorescence, a branched cluster of individual flowers. Begonias are an example of this type. Those flowers that grow at the base of a leaf where it attaches to the stem of the plant are called axillary flowers. Snapdragons are an example of axillary flowers.

There are four concentric whorls (rings) of organs in a complete flower. From the center to the outside, they are the pistil, stamens, petals, and sepals. Fundamentally, these four parts are modified leaves.

The pistil, a long stalk arising in the center, is the female reproductive organ of a flower. It is composed of the stigma, style, and ovary. The stigma is the sticky knob at the outer end of the stalk. The style is the portion of the stalk connecting the stigma to the ovary. The ovary is the round base that contains one or more undeveloped seeds called ovules. In each ovule is an egg waiting to be fertilized by a sperm.

Stamens, the male reproductive organs, also arise from the center of the flower and encircle the pistil. The stamens are composed of a stalk, called a filament, topped by an anther. The anther produces many microscopic pollen grains. The male sex cell, a sperm, develops within each pollen grain.

Petals, the often-brightly colored portion surrounding the pistil and stamens, are a flower's showpiece. They attract the attention of passing insects, birds, and people. The layers of petals in a flower comprise the corolla.

Sepals lie below the petals and are usually green and leaflike in appearance. Sepals form a temporary, protective cover over an unopened flower. When the petals of a flower are ready to unfurl, the sepals fold back.

In some species, one or more of the four whorls of floral organs is missing, and the flower is referred to as an incomplete flower. A bisexual flower is one with both stamens and a pistil, whereas a unisexual flower is one that has either stamens or a pistil, but not both. All complete flowers are bisexual since they have all four floral whorls. All unisexual flowers are incomplete since they lack either stamens or a pistil.

Pollination

In angiosperms, pollination is the transfer of pollen from an anther to a stigma. Pollen grains land on the sticky stigma, where they begin to germinate or grow. A pollen tube then forms down the style, sperm is delivered to the ovules, and fertilization takes place.

If the transfer of pollen occurs between an anther and the stigma of the same plant, it is known as self-pollination. Complete flowers are able to self-pollinate. When the transfer of pollen occurs between an anther and the stigma of different plants, it is known as cross-pollination. Of the two methods, cross-pollination produces stronger and healthier off-spring since it mixes up the genetic make-up of plants. Cross-pollination can be brought about by wind, rain, mammals, birds, and insects.

Pollination by wind. Many angiosperms are pollinated by wind. Wind-pollinated flowers, such as those of corn and all grasses, tend to have a simple structure lacking petals. The anthers dangle on long filaments, allowing the light pollen grains to be easily caught by the wind. The stigma are freely exposed to catch the airborne pollen. Large amounts of pollen are usually wasted because they do not reach female reproductive organs. For this reason, most wind-pollinated plants are found in temperate regions, where members of the same species often grow close together.

Pollination by animals. In general, pollination by insects and other animals is more efficient than pollination by wind. Many times flowers

offer "rewards" to attract these animals—sugary nectar, oil, solid food, a place to sleep, or even the pollen itself. Generally, plants use color and fragrances to lure their pollen-transporting agents.

The flowers of many species of plants are marked with special pigments that absorb ultraviolet light (light whose wavelengths are shorter than visible light). These pigments are invisible to humans and most animals. But the eyes of bees are sensitive enough to detect the patterns created by the pigments and so the bees are drawn to them.

Having been attracted to a flower, an insect or other small animal probes inside for its reward. In doing so, it brushes against the anthers and picks up dust pollen on its body. When the animal moves on to the next flower, it brushes past the stigma, depositing pollen. Many flowers are designed precisely to match the body forms of the animals participating in this pollen transfer. In this way, contact with both the anthers and the stigma is ensured. A few orchids use a combination of smell, color, and shape to mimic the female of certain species of bees and wasps. The male bees and wasps then try to mate with the flower. In the process, they either pick up or transfer pollen to that flower.

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flower

The Columbia Encyclopedia, 6th ed.

Copyright The Columbia University Press

flower, name for the specialized part of a plant containing the reproductive organs, applied to angiosperms only. A flower may be thought of as a modified, short, compact branch bearing lateral appendages. Like twigs, flowers develop from buds, and the basic floral parts (sepal, petal, stamen, and carpel) are in actual fact greatly modified leaves. A typical flower is a concentric arrangement of these parts attached at their base to the receptacle, the tip of the stem. Outermost is a whorl of leaflike green sepals (the calyx) encircling a whorl of usually showy, colored petals (the corolla). Within the corolla the stamens, bearing anther sacs full of pollen, surround the central carpels (ovary). Inside the ovary at the base of the pistil are the ovules, containing the female sex cells; after fertilization of the egg, the ovule becomes the seed and the ovary becomes the fruit. The ovary and stamens are termed essential flower parts, the petals and sepals accessory parts. The number and arrangement of the floral organs vary considerably among the many families and orders of plants and are used in the classification of plants; they also indicate the degree of evolution of the plant. In general, the higher a plant is on the evolutionary scale, the greater is the flower's complexity. The basic number of parts differs from class to class and from family to family; in monocotyledonous plants the parts generally occur in groups of three or in multiples of three, and in dicotyledons more often in groups of two, four, and five. Flowers may be staminate (lack carpels), carpellate, or both; staminate and carpellate flowers may appear on the same plant, on separate plants, or in the same inflorescence. One type of inflorescence, characteristic of the parsley family, is the umbel, in which the tiny florets are borne on separate stalks radiating out from the stem tip. Sometimes the parts serve unusual purposes: the true flowers of the dogwood and the poinsettia are inconspicuous, and the showy
"petals"
are really modified leaves called bracts. In the jack-in-the-pulpit the florets are clustered on a spike canopied by a large bract, the spathe; the hood of the lady's-slipper, on the other hand, is a modified sterile stamen. Grass inflorescences are tiny spikelets sheathed by protective scales called glumes (the chaff or grain). Flowers have been cultivated and bred for their beauty and their perfume from earliest times and have accumulated a vast and intricate treasury of symbolic associations derived from legend and folklore. Individual flowers have been celebrated in heraldry (rose), in religion (lotus), and in politics (violet) and have become emblems for many countries, including Switzerland (edelweiss), France (fleur-de-lis), Scotland (thistle), the Netherlands (tulip), and the United States (see state flowers).

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flower

flower The structure in angiosperms (flowering plants) that bears the organs for sexual reproduction. Flowers are very variable in form, ranging from the small green insignificant wind-pollinated flowers of many grasses to spectacular brightly coloured insect-pollinated flowers. Flowers are often grouped together into inflorescences, some of which (e.g. that of dandelion) are so compacted as to resemble a single flower. Typically flowers consist of a receptacle that bears sepals, petals, stamens, and carpels (see illustration). The flower parts are adapted to bring about pollination and fertilization resulting in the formation of seeds and fruits. The sepals are usually green and leaflike and protect the flower bud. The petals of insect-pollinated flowers are adapted in many ingenious ways to attract insects and, in some instances, other animals. For example, some flowers are adapted to attract short-tongued insects by having an open shallow corolla tube and nectar situated in an exposed position. Flowers adapted for pollination by long-tongued insects have a long corolla tube of fused petals with nectar in a concealed position. The tongue of the insect brushes against the anthers and stigma before reaching the nectar. Wind-pollinated flowers, in contrast, are inconspicuous. The anthers dangle outside the corolla and the stigmas have a feathery surface to catch the pollen grains.

Some species are adapted for self-pollination and have small flowers, no nectar, and stamens and carpels that mature simultaneously.

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flower

flow·er
/ ˈflou(-ə)r/
•
n. Bot.
the seed-bearing part of a plant, consisting of reproductive organs (stamens and carpels) that are typically surrounded by a brightly colored corolla (petals) and a green calyx (sepals). ∎
a brightly colored and conspicuous example of such a part of a plant together with its stalk, typically used with others as a decoration or gift:
I stopped to buy Bridget some flowers. ∎
the state or period in which a plant's flowers have developed and opened:
the roses were just coming into flower.•
v. [intr.]
(of a plant) produce flowers; bloom:
these daisies can flower as late as October. ∎ fig.
be in or reach an optimum stage of development; develop fully and richly:
it is there that the theory of deconstruction has flowered most extravagantly |
[as n.] (flowering)
the flowering of Viennese intellectual life. ∎
[tr.]
induce (a plant) to produce flowers.
PHRASES:the flower of1.
the finest individuals out of a number of people or things:
the flower of college track athletes.2.
the period of optimum development:
a young policeman in the flower of his life gunned down.DERIVATIVES:flow·er·less
adj.flow·er·like
/ -ˌlīk/ adj.

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flower

flower Reproductive structure of a flowering plant. It has four sets of organs set in whorls on a short apex (receptacle). The leaf-like sepals protect the bud and form the calyx. The brightly coloured petals form the corolla. The stamens are stalks (filaments) tipped by anthers (pollen sacs). The carpels form the pistil, with an ovary, style and stigma. Flowers are bisexual if they contain stamens and carpels, and unisexual if only one of these is present. Reproduction occurs when pollen transfers from the anthers to the stigma. A pollen tube grows down into the ovary where fertilization occurs and a seed is produced. The ovary bearing the seed ripens into a fruit and the other parts of the flower wilt and fall.

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flower

flower In angiosperms, the structure concerned with sexual reproduction, consisting of the androecium (male organs) and gynoecium (female organs), commonly surrounded by a corolla (petals) and calyx (sepals). The male and female parts may be in the same flower or in separate flowers. In many plants the term ‘flower’ is popularly applied to an inflorescence that in fact comprises numerous small flowers (florets) grouped together.

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